As Many Questions as There are Buildings

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In olden days (2013), Urban Green Council brought forth a report called 90 by 50, which showed in some detail that a 90 percent reduction in greenhouse gas emissions was possible in New York City using off-the-shelf technology—and at a cost that would be acceptable if financed over twenty-five years.

90 by 50 found that New York City will have to reduce energy loads by at least 50 percent in buildings, some 80 percent of which would be today’s buildings. The 90x50 model assumed rigorous building retrofits, with high levels of energy-saving technologies such as air sealing, heat recovery ventilation and insulation, as well as high-efficiency lighting and electric appliances.

But this still left significant heating and cooling loads. To meet these loads, we modeled a 2050 New York City filled with all-electric buildings. This solution yielded an overall reduction in source energy of 55 – 60 percent if powered by 2010’s generation mix. However, adding a carbon-neutral electric grid gave us a building sector with no greenhouse gas emissions.

What would these buildings look like?

Let’s tackle heating first since it consumes over a third of building energy in NYC. Electric resistance heat is simple (think of a house heated by a giant toaster). But heat pumps—because they move heat around, rather than create heat—provide three times the heat per kilowatt-hour. Since heat pumps provide cooling as well, we envisioned a 2050 New York City providing heating, cooling and hot water to everyone using heat pumps.

But what sorts of heat pumps? We modeled heat pumps in the buildings of the future based on a mix of air-source (system that transfers heat from outside air to inside a building and vice versa) and ground-source (system that takes advantage of the relatively constant year-round ground temperature to pump heat to or from buried pipes), with air-source in-building heat pumps for domestic hot water.

In the real future, there will be as many questions as there are buildings, a few of which are:

In multifamily buildings, what’s the best mix of central versus distributed HVAC units in each apartment?

What about those pesky steam-heated buildings? They constitute almost three-fourths of NYC’s current building stock. The problem: steam systems cannot be converted to heat pumps, and will still be burning gas in the future. We need an exit strategy starting today: no more replacement steam boilers. When steam boilers die, replace them with hot water systems or heat pumps.

Rooftop photovoltaics are a no-brainer where possible, but what about cogeneration? Using natural gas to generate electricity and hot water on site can reduce a building’s carbon footprint, but will that still be true when the grid gets greener? Is cogen only a transitional technology, or will it become a more permanent part of the landscape?

Another big problem is how we will get power up into NYC’s buildings. Much of the wiring in older buildings will need to be upgraded or replaced. That’s a lot of copper! Can we find ways to use aluminum wire safely in buildings? It carries all the power crisscrossing the country in high voltage transmission lines.

And we will need a lot of carbon-free electricity. The 90 by 50 model, with its dramatically reduced loads, estimated the city’s all-electric buildings would consume approximately the same annual electric energy as they do today. These dramatic load reductions mean that generating the amount of carbon-free electric energy needed would be achievable, if not easy.

The result for electric energy sounds great, but there’s a catch: Today we have a strong summer electric demand peak, driven by air conditioning, sometimes causing blackouts. In an all-electric 2050, this will shift to a peak driven by heating that will be substantially larger than today’s summer peak. It will occur in the wee hours of January mornings when photovoltaic power is not available. This raises more questions: Can we lower the peak with thermal storage in buildings? Can we install gigawatts of electro-mechanical or battery storage? How much at the utility level and how much in buildings? What’s the schedule?

There are no easy answers and few inexpensive answers. We have the knowledge and tools we need—our task is to decide how best to use them. We have to figure this out—our civilization depends on it. On October 4, It’s Electrifying will advance the conversation.

INTERESTED IN HEARING MORE ABOUT 90 BY 50?

About the author

Richard Leigh

Richard Leigh is a Visiting Professor of Physics at Pratt Institute, primarily teaching courses in building science. He formerly served as Urban Green's Director of Research, where he managed research projects including the 2016 New York City Auditing and Benchmarking Report for 2013 data and 90 by 50, showing that New York City can reduce its greenhouse gas emissions 90 percent below current levels by 2050.